Evaluation of the Acute Abdomen Evidenced-based Testing Strategies

1. Evaluation of the Acute AbdomenEvidenced-based Testing Strategies Thomas W. Lukens MD PhD FACEP MetroHealth Medical Center Cleveland, OH Associate Professor of Emergency Medicine Case Western Reserve University School of Medicine

2. Greetings from Cleveland, OH

3. The Acute Abdomen • Pain less than one week • Sudden onset • Surgery needed • Peritonitis • Severe pain Any condition that needs rapid decision making and/or operative intervention

4. ABDOMINAL PAIN Emergency Department: • Undifferentiated patients • A collection of symptoms and signs are gathered to predict the conditional probability of a diagnosis • Traditional teaching is the reverse • Few evidenced based studies in undifferentiated conditions

5. ABDOMINAL PAINEmergency Department Series DischargeDiagnosis 1972 1977 1993 Undifferentiated (UDAP) 41% 39% 25% GI causes 13% 19% 18% Gastroenteritis 7% 12% 5% Surgical GI 10% 18% 8% UTI 11% -- 11% Pelvic Disorder 12% -- 12% Admission rate 27% 42% 18% Ref:Brewer, Am J Surg, 1976; Jazon, AC Scand, 1982; Powers, AJEM, 1995

6. Acute AbdomenTesting • History and Physical Examination • Serial examinations • Laboratory • WBC • Urinalysis/pregnancy test • Plain Radiography • CT • Ultrasound • Color flow Doppler • Nuclear Medicine • MRI

7. Acute AbdomenHistory & Physical Examination • Intraabdominal • 3 G’s-- GI, GU, GYN • Vascular • Extraabdominal • Cardiovascular • Metabolic • Abdominal wall • Neurogenic

8. Acute AbdomenHistory & Physical Examination • Accuracy is lacking at times • Atypical presentations • Missed findings • Appendicitis • 50-87% sensitive • false positive = negative laporatomy • false negative = perforation • Acute Abdominal Aneurysm (AAA) • < 50% sensitive • Diverticulitis - 34% sensitivity • LR+ = 2-3, LR- = 0.4 Bergeron, Am J Surg, 1999;177:460, Chervu Surg 1995;117:454, Korner, World J Surg 1997;21:313

9. Likelihood ratios A way to measure performance • LR of positive test: sensitivity of test/1-specificity • LR of negative test: 1-sensitivity/specificity • LR+ - the likelihood of the test being positive in a patient with the disorder, compared to the likelihood of a positive test in someone without the disorder • LR-the likelihood of a negative test in someone with the disorder compared to a negative test in one without the disorder

10. Likelihood ratiosCalculating probabilities • LR times the (estimated) pretest probability = post test odds of the disease • Appendicitis- all ED abdominal pain patients • Estimated pretest probability ~ 4% • LR+ of the “test” ~4, LR- is 0.3 If all received the test for appendicitis (4 X 1:25) = ~16% chance that a positive test is actually detecting appendicitis in the patient. If negative test (0.3 x 1:25), there is still a 1.2% probability of patient having appendicitis (lowered pre-test probability by about a third) Not a particularly accurate test in undifferentiated patients

11. Acute AbdomenLaboratory testing • WBC - limited utility • WBC > 11,000 LR+ = ~ 2 < 11,000 LR- = ~ 0.5 • WBC alone doesn’t distinguish patients with surgical disease from non-specific abdominal pain • Urinalysis • AAA - misleading • Hematuria in up to 30% with AAA • Most common misdiagnosis in AAA- kidney stone • Renal colic - hematuria • LR+ ~ 2 , LR- = 0.3

12. Acute AbdomenLaboratory testing • Liver function tests • Normal in up to 40% with acute cholecystitis • Not specific for any disease entity • Amylase/Lipase • Often normal in active pancreatitis • Sensitivity ~60%

13. Acute AbdomenImaging • Plain films- provide little in addition to H & P • Few specific findings • Sensitive for free air 90-95% • Bowel obstruction- 70% sensitive (LR+ ~3, LR- 0.6) • Appendicitis • LR+ = 1 • LR- = 0.4 • Cholecystitis • LR+ = 2 • LR- = 0.5 Frager, AJR, 1994,162:37, Gruber, Ann Emerg Med, 1996,28:273, Izbicki, Eur J Surg,1992,158:227,

14. Acute AbdomenImaging-CT CT- test of choice in most abdominal conditions LR+LR- • Appendicitis Unenhanced focused 29 0.1 Contrast focused 49 0.02 Abdomen/pelvis (contrast) 18 0.1 • Small bowel obstruction 22 0.1 low grade 3 0.5 • Diverticulitis 98 0.02

15. Acute AbdomenImaging-CT LR+LR- • AAA 19 0.03 • Renal colic (Unenhanced) 32 0.02 • Mesenteric ischemia • CT angiography 5 0.3 • MRA enhanced gadolinium 8 0.2 • Biliary tract (stones) 28 0.2 • Common duct 8 0.3 • MR cholangiography 320.05

16. Acute AbdomenImaging-Ultrasound LR+LR- Biliary tract (stones)300.1 • Cholecystitis 29 0.1 • Common duct obst 11 0.1 • Common duct stone 8 0.2 • HIDA scan 10-200.05 • AAA (nonleaking) 9 0.1 • Diverticulitis 18 0.2 • Appendicitis 11 0.5 • Ectopic TVS (BHGC>1500)80 0.2

17. Appendicitis - CT Liberal use of CT has lowered negative appendectomy rate to 5.4% Peck, Am J Surg 2000;180:133 CT for appendicitis has lowered hospital stay by 1/2Raptopoulos, Radiology 2003;226:521 Appendicitis - most common operation but accuracy hasn’t changed significantly in past decade(data through 1999) Flum, JAMA 2001;286:1748

18. Appendicitis - CT Use in equivocal cases- not high or low probability patients- not routinely Ujiki, J Surg Research 2002;105:119 Call for a surgeon not a CT- more cost effective and accurate to have the surgeon see the patient first Morris. Am J Surg, 2002;183:547

19. Acute Abdominal Pain -Imaging • History & examination and simple lab tests have about a 50-60 % accuracy (initial to final diagnosis) • Technological advances in imaging are responsible for our increased accuracy in diagnosing patients with acute abdominal pain Helical CT Ultrasound by EM physicians 24/7 MRI

20. Good judgment comes from experience, and a lot of that comes from bad judgment.Will Rodgers